Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/12—Powdering or granulating
  • C08J3/124—Treatment for improving the free-flowing characteristics
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2321/00—Characterised by the use of unspecified rubbers

Definitions

• This invention relates to rubber powders and methods for making and using rubber powders. More particularly, it relates to powders made of rubber particles coated with non-tacky materials and methods of converting bale rubber by mechanical action to rubber powders-comprised of such coated particles.
• Patents have also issued in the general area of rubber powder; see, for example, U.S. Patent 4,032,501 to Schulz which describes a method for producing rubber powders from hydrocarbon solution rubber, carbon black and foam inhibiting surfactants.
• Other patents dealing generally with this field include U.S. Patent Nos. 2,777,008; 3,245,945; 3,203,922; 3,060,145 and 3,251,798.
• the rubber powders of this invention comprise substantially nonvulcanized rubber particles having an average particle size of less than about 10 mm and coated with an effective amount of an anti-tack agent.
• An effective amount of anti-tack agent is an amount rendering the surface of the particle non-tacky; on a macroscale such an amount manifests itself as rendering the rubber powder resistant to agglomeration and cold flow.
• the powders of this invention are free flowing and do not require substantial post-blending shear to achieve acceptable filler dispersion.
• the invention also includes a direct mechanical method for producing uncured rubber powder which comprises mixing bale or slab rubber and an anti-tack agent at a temperature above the glass transition temperature of the rubber under conditions of high mechanical action for a time sufficient to produce the powder of the invention.
• a direct mechanical method for producing uncured rubber powder which comprises mixing bale or slab rubber and an anti-tack agent at a temperature above the glass transition temperature of the rubber under conditions of high mechanical action for a time sufficient to produce the powder of the invention.
• An important aspect of this method is that the bale rubber is first subdivided in a premixing step into segments having a maximum particle size of less than about 20cm and combined with the anti-tack agent to form a homogeneous aggregate before it is subjected to mechanical action and high shear.
• the anti-tack agent used comprises a component to be later compounded with the rubber to make a vulcanizate such as carbon black, talc, silica, clay and the like.
• rubber powder is formed without the need of latex or solution steps.
• the powder is formed directly and mechanically from bale or slab rubber without the intervention of latex or solution procedures.
• it is also an advantage of this method that it is carried out at a temperature above the glass transition temperature of the rubber and thus does not require cryogenic techniques. Such techniques demand large investments of energy to, maintain severely reduced temperatures.
• the rubbers used in the present invention generally include elastomers of both the natural and synthetic type.
• Natural elastomers include Hevea and Guayule rubbers and other rubbers isolated from plant sources as well as blends thereof. Chemically modified natural rubbers such as hydrogenated, chlorinated and sulphonated natural rubbers can also be used.
• Synthetic rubbers include a wide range of materials such as those designated in the ASTM standard recommended practice for rubber and rubber latice nomenclature; see ANSI/ASTM DY1418-79a. These include saturated, polymethylene synthetic rubbers such as those made from acrylates and alpha-olefin polymers, as well as related co-polymers such as ethylene propylene types (EPM or EPR), terpolymers of various types such as EPDM, perfloro rubber (FKM and FFKM), oxygenated rubbers containing oxygen in the polymer chain, such as those made from ethylene and propylene oxide (CO, ECO, and GPO types), the sulphur analogs thereof, phosphazene rubbers and silicone rubbers.
• EPM or EPR ethylene propylene types
• FKM and FFKM perfloro rubber
• CO, ECO, and GPO types oxygenated rubbers containing oxygen in the polymer chain, such as those made from ethylene and propylene oxide (CO, ECO,
• Rubbers containing carbon, oxygen and nitrogen in the polymer chain can also be used in the invention.
• Hydrogenated and other types of chemically treated synthetic rubbers are also useful, such as hydrogenated BR, chlorinated BR, bominated BR, etc.
• a particularly useful class of rubbers are the "R" class, which contain unsaturation in the main chain and include both natural rubber types and synthetic rubber types. These R class rubbers include the following:
• Both solution and emulsion prepared rubbers can be used in making the powders of this invention.
• Blends of two or more of the various rubber types noted may also be used.
• Non-limiting examples of such blends are SBR/NR (50/50), Guayule/Hevea (20/80), IR/hydrogenated BR (33/67), EPDM/BD (60/40), CHR/BHR (35/65), etc.
• the rubber used to make the powders of this invention is substantially non-vulcanized (i.e., substantially uncured or uncross-linked). This means that the rubber is not vulcanized at all or is vulcanized to such a low degree that it behaves as if it were not vulcanized, particularly with respect to its tack and facile processing properties. Such lightly vulcanized materials are sometimes said to be prevulcanized. Such prevulcanization can be effected by low levels of high energy radiation.
• an effective amount of an anti-tack agent is that amount which prevents agglomeration of the powder under the conditions of its formation and storage. Typically, this amount will be about 10-300 parts anti-tack agent per 100 parts rubber (phr).
• anti-tack agent usually the amount of anti-tack agent will vary directly with the inherent tack of the rubber used to make the powder and inversely with the average size of the rubber particles comprising the powder since the rubber surface area will also vary inversely with particle size. Often about 30-100 phr anti-tack agent is used.
• These materials increase the hardness, stiffness, strength, and resistance to tear and abrasion of the vulcanized rubber compound and include a wide range of carbon blacks, zinc oxide, fine particles of percipitated calcium carbonates, hard clays, hydrated silica compounds, such as calcium silicate and silicon dioxide and, in some specialized instances, organic materials such as finely divided phenolic resins.
• abrasives such as pumice, tripoli and carborundum are used as filler components and can also be used as anti-tack agents in the powders of this invention.
• white and colored material such as mineral pigments and organic dyes may be useful.
• the anti-tack agent of choice is one of the well known carbon blacks which are used as fillers and reinforcing agents in rubber compounds intended for ultimate use in tire and rubber article manufacture.
• the rubber powders of the present invention are generally produced by direct mechanical means without the intervention of emulsions or solutions. That means that there is no need to go through a latex-forming or solution step as is used in many processes of the prior art.
• cryogen techniques are not used necessarily in making the powders of this invention.
• the powders of this invention are made by mechanical, non-solvent, non-emulsion, non-cryogenic, non-chemical treatment, non-special additive techniques.
• One convenient technique for producing the rubber powders of this invention is by mechanical shearing of rubber and anti-tack agents under specified conditions of high shear, preceded by a premixing stage in which a homogeneous aggregate of subdivided slab or baled rubber and anti-tack agent is formed. While it is not necessary to understand any theoretical concept or explanation of the invention to practice it, it may be interesting to consider a hypothetical analysis of the process. In this analysis any mixing process is considered to involve two simultaneous events. One, entails the shear-induced subdivision of the material and the other, its coalescence after subdivision.
• coalescence-preventing techniques One is cooling in which the material such as rubber becomes a rigid plastic whose surface ceases to be tacky.
• Another method of preventing coalescence of rubber particles would be to cover them with an anti-tack agent, a procedure somewhat analogous to-the well-known technique of microencapsulation. In this instance, however, small particles of anti-tack agent are used to surround:and prevent coalescence of the relatively larger rubber particles by acting as a barrier.
• the bale or slab rubber from which the powder is to be made is first subdivided and more or less intimately mixed with the anti-tack agent before the resulting homogeneous aggregate is subjected to mechanical action which affects the final subdivision of the rubber to particles of increasing fineness.
• this initial subdivision of the rubber is carried out so as to produce particles of an average size of about 0.2-20 cm, say about 0.5-10 cm, usually about 0.75-5.0 cm.
• Subdivision initially can be carried out by any convenient technique such as low shear extrusion and chopping, rough grinding, cutting, stamping and the like.
• the anti-tack agent is combined with the initially subdivided rubber and mixing is carried out to provide a homogeneous aggregate.
• This homogeneous aggregate can then be processed directly and mechanically under conditions which progressively break down the rubber particles to a size of less than about 1 cm.
• the resultant rubber powder has an average particle size of about 0.01-20 mm, typically about 0.1-10 mm. It should be noted that not all the anti-tack agent present in the rubber powder need be attached to the rubber particle surface. Free unassociated anti-tack agent may be present.
• bale or slab rubber/anti-tack agent for example,:filler
• this machine comprises a mixing and plasticating cylinder and a mixing and plasticating rotor with passages therein, the shaft of said mixing and plasticating rotor being connected to a rotary drive outside said cylinder.
• the mixing and plasticating cylinder and the mixing and plasticating rotor are axially movable in relation to each other.
• the Nielander machine accomplishes mixing and formation of the powders of this invention at controlled pressure, friction and shear conditions.
• the actual reduction of rubber particles to powder may occur by cutting, abrasion or shear-induced elongation and subsequent rupture of the particles or two or more of these in concert.
• one method of making the powders of this invention is wherein the mixing is accomplished by a machine for mixing rubber and other highly viscous materials that control pressure, friction and shear conditions, which comprises a mixing and plasticating cylinder and a mixing and plasticating rotor with aperture passages, the shaft of said mixing and plasticating rotor being connected to a rotary drive outside the mixing and plasticating cylinder, said mixing and plasticating rotor and said mixing and plasticating cylinder being axially movable in relation to each other, during said relative motion of said mixing and plasticating rotor and said mixing and plasticating cylinder, the internal wall area of said mixing and plasticating cylinder being scrapped off by said mixing and plasticating rotor and the contents (i.e., the rubber/anti-tack agent aggregate) of said mixing and plasticating cylinder being pressed through the passages of said mixing and plasticating rotor at friction and shear.
• a machine for mixing rubber and other highly viscous materials that control pressure, friction and shear conditions which comprises a mixing and plasticating cylinder and
• the direct mechanical conversion of bale rubber to rubber powder according to this invention occurs at ambient or slightly elevated temperatures (the elevation is usually the result of the mixing or related processes). These temperatures range from about -20-150° C, typically about 0-80° C.
• the conversion process is carried out for a time sufficient to produce the powder; usually this time is about 0.1-10 minutes. Excessively long conversion times sometimes leads to compaction of this powder and should be avoided.
• application of shear to the admix of rubber and carbon black such as occurs in internal mixers, of the Banbury and IMI type, usually lead to formation of a compacted stock in which the carbon black and rubber are well distributed. In such compacted stocks, the carbon black is also dispersed in the rubber on a mic-roscale. When, however, the herein disclosed conditions areopresent rubber powders are formed.
• the abrasive quality of the anti-tack agent such as carbon black may contribute to breakdown of the rubber particle.s.
• apertures such as the slots found in the piston of the IMI machine may cause breakup of the particles and/or function to allow removal of the particles from the zone of their formation.
• Rubber powders were made in a 3 litre Nielander mixer according to U.S. Patent 3,623,703 and available from Schiesser AG of Switzerland.
• the mixer has a cylindrical steel chamber having a capacity of about 3 litres.
• a close-fitting round piston having several radial slots can be moved back and forth in the chamber with speeds ranging from approximately 0 to Sm/minute. This piston can be simultaneously rotated at speeds up to 300 rpm.
• the chamber is charged with rubber, anti-tack agent (such as carbon black) and any other desired ingredients, closed and the piston activated. Motion of the piston results in pumping of the rubber, anti-tack agent and other ingredients present from one side of the chamber to the other.
• anti-tack agent such as carbon black
• the aforedescribed mixer was charged with 1100 grams of SBR.
• the piston speed was set at 1.5-2m/minutes and the rotation at 280 rpm.
• the rubber was premixed for one complete piston cycle.
• 504 grams of N 339 carbon black were added. Water flow to the cooling units at the chamber, back and front cover and the rotor was adjusted to rates of approximately 3/3/3 and 7 litres per minute, respectively. Mixing was then continued under these conditions for two minutes to produce a free flowing rubber powder.
• a series of powder preparations is made varying carbon black type, rubber type, and the size of the rubber pieces in the premix stage. These variations are described in Table I.
• a standard procedure is used as follows: Rubber of the indicated type, 1100 grams, is divided into rough cubes of the indicated size (on an edge). These cubes are combined with the carbon black of the indicated type, 504 grams, in an appropriately sized bag and tumbled at 25° C by hand to thoroughly mix the ingredients. The combined mixture is then charged to the above-described Nielander machine and processed under essentially the same conditions. Comparative Example K
• Example A The cooling rate for the rotor was increased by a factor of approximately two-fold over that in Example A.
• the piston speed and rotation rate were kept the same.
• Five hundred fifty grams of SBR was charged to the chamber of the Nielander machine and premixed for one complete piston cycle.
• 504 grams of carbon black was added and mixing was carried out for one minute.
• a rubber powder ⁇ esulted.
• To this powder was added 275 grams of additional rubber. Mixing was continued for another 0.5 minute, then an additional portion of 275 grams of SBR was added, and mixing continued for 0.5 minutes. At this point the rubber/carbon black charge was compacted. Further mixing at a piston speed of 3-3.5m/minutes for two more minutes produced a fully compacted rubber whose temperature upon removal from the machine was 160°C.
• Example A It is clear from a comparison of the results of Example A and Example K that prolonged mixing of the rubber powder under conditions of high shear leads to compaction of the powder. Thus, it is seen that it is only necessary to subject the rubber/anti-tack agent aggregate to mechanical action for a period sufficient to produce powder. Typically, this period ranges from about 0.1-10 minutes. It may vary somewhat depending on the design of the equipment and conditions applied during the mechanical action.
• the powder prepared according to this invention was further mixed in a Brabender Plasticorder for two, four and eight minutes (120°C jacket temperature and 60rpm) and the materials subsequently molded into 6x 6x 0.080 . plaques.
• Stocks of identical composition were prepared from the same basic raw materials in the Brabender under essentially identical conditions using mixing times of six and eight minutes, respectively. These stocks were also molded into 6x 6x 0.080" plaques and radiation vulcanized along with the former plaques to a dose of 10 Mrad.
• the carbon black dispersion and physical properties of these plaques are shown in Table II. It should be noted that the stocks made from the powder and mixed for six minutes had essentially identical carbon black dispersion and physical properties, that is modulus, tensile strength and energyoto break, as those of stocks prepared from raw AI using a total mixing time of eight minutes.
• the powders of this invention can be shaped and vulcanized into a variety of useful rubber articles using known techniques such as extrusion, molding and the like.
• articles that can be made from the powders are tires, hoses, seals, cables, belts and similar goods.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Processes Of Treating Macromolecular Substances (AREA)

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• 1983
  • 1983-06-21 CA CA000430856A patent/CA1226178A/fr not_active Expired
  • 1983-06-22 ZA ZA834574A patent/ZA834574B/xx unknown
  • 1983-06-24 AU AU16221/83A patent/AU559991B2/en not_active Ceased
  • 1983-06-28 DE DE8383106303T patent/DE3380595D1/de not_active Expired
  • 1983-06-28 EP EP83106303A patent/EP0100434B1/fr not_active Expired
  • 1983-06-28 NZ NZ204734A patent/NZ204734A/en unknown
  • 1983-07-12 JP JP58125629A patent/JPS5924734A/ja active Pending
  • 1983-07-13 ES ES524080A patent/ES524080A0/es active Granted
  • 1983-07-13 PH PH29216A patent/PH18673A/en unknown
  • 1983-07-13 BR BR8303738A patent/BR8303738A/pt unknown
  • 1983-07-13 MX MX198012A patent/MX163965B/es unknown
  • 1983-07-14 PT PT77028A patent/PT77028B/pt not_active IP Right Cessation

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